Cleaner head assembly for a vacuum cleaner

ABSTRACT

A cleaner head assembly for a vacuum cleaner includes a cleaner head body pivotably attachable to a main body of a vacuum cleaner and a brush housing pivotably mounted on the cleaner head body, the brush housing having a suction opening, a brush bar mounted therein and a resilient member provided to bias the brush housing in a pivoting direction so as to urge a rear portion of the brush housing in an upward direction with respect to the cleaner head body. This configuration allows the brush housing to be doubly articulated with respect to the main body of the vacuum cleaner as it is biased by the resilient member in the pivoting direction such that the rear portion of the brush housing is urged in an upward direction with respect to the cleaner head body and the suction opening remains in a horizontal plane.

REFERENCE TO RELATED APPLICATIONS

This application is a national stage application under 35 USC 371 of International Application No. PCT/GB2007/002701, filed Jul. 16, 2007, which claims the priority of United Kingdom Application No. 0615683.0, filed Aug. 8, 2006, the contents of which prior applications are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a cleaner head assembly for a vacuum cleaner.

BACKGROUND OF THE INVENTION

An upright vacuum cleaner normally comprises a main body containing dirt and dust separating apparatus, a cleaner head rotatably mounted on the main body and having a dirty air inlet, and a motor and fan unit for drawing dirty air into the dirt and dust separating apparatus via the dirty air inlet so that dirt and dust can be separated from the airflow before the clean air is expelled to the atmosphere. The dirty-air inlet or suction opening through which dirty air is sucked into the vacuum cleaner is directed downwardly so that it faces the floor to be cleaned. The dirt and dust separating apparatus can take the form of a filter, a filter bag or, as is known, can take the form of a cyclonic arrangement. The present invention is not concerned with the nature of the dirt and dust separating apparatus and is therefore applicable to vacuum cleaners utilising any of the above arrangements or another suitable separating apparatus.

A brush bar is supported in the dirty air inlet so that it protrudes to a small extent from the inlet. The brush bar is activated mainly when the vacuum cleaner is used to clean carpeted surfaces. The brush bar comprises an elongate cylindrical core from which bristles extend along its length in a radial direction. The brush bar is driven by the motor via a drive belt, or by a direct drive motor so that the brush bar rotates within the inlet. Rotation of the brush bar causes the bristles to sweep along the surface of the carpet to be cleaned to loosen dirt and dust and pick up debris. The suction of air causes air to flow around the brush bar and underneath it to help lift the dirt and dust from the surface to be cleaned and then carry it from the dirty air inlet or suction opening to the dirt and dust separating apparatus.

It will be appreciated that the effectiveness of an upright vacuum cleaner will depend upon the amount of dirt and dust which can be picked up by the cleaner head and passed to the dirt and dust separation apparatus. For each vacuum cleaner there is an optimum configuration for the relationship between the dirty-air inlet and the carpet to be cleaned. Very often, the relationship will be one that maintains the dirty-air inlet in a plane which is parallel to the floor so that the mouth of the inlet is horizontal. Ideally then, the suction opening or dirty air inlet should be maintained completely horizontal to the floor (or at the optimum angle or configuration) so that the maximum amount of air sucked into the dirty air inlet travels through the fibres of the carpet being cleaned before travelling on through the cleaner to the dirt and dust separating apparatus. However, the angle of inclination of the cleaner head to the surface may differ when the vacuum cleaner is used on different types of floor surface, eg on carpets with different piles and textures. Also, the vacuum cleaner is in use moved over the surface to be cleaned in reciprocating forwards and backwards movements so that the cleaner head travels both forwards and backwards over the surface whilst collecting dust and dirt via the dirty air inlet. In most cases the cleaner head will be acted upon in different ways by the carpet when it is travelling in different directions and will not maintain good contact on all sides of the dirty air inlet in both directions. Furthermore, the action of the user can result in the angle of inclination of the handle to the vertical being varied quite significantly during normal use and this can cause the plane of the dirty air inlet to be lifted, either at the front or the back, away from the optimum configuration. The weight and the mounting arrangement of a separate brush bar motor on the cleaner head may also contribute to the cleaner head not maintaining good contact with the surface to be cleaned and moving away from the optimum configuration of the dirty air inlet. Any and all of these things can result in a reduction in the effectiveness of the suction of the cleaner head which can lead to a loss in the maximum level of pick-up and then to customer dissatisfaction.

Some attempts have been made to solve this problem by way of manually operated cleaner head lifting and lowering mechanisms by means of which the user is able to set the optimum height for the cleaner head when the cleaner is being used on a particular surface. However, these mechanisms only lift and lower the cleaner head by pivoting about the axis about which the cleaner head is connected to the main body of the cleaner. They do not address the problem of the dirty air inlet becoming inclined to the optimum configuration and thereby allowing the inlet suction to become less effective. One effective way to address this problem has been described in EP1043947 which describes a cradle-type arrangement for mounting the brush bar in the dirty air inlet. The brush bar is mounted in a cradle which is itself freely rotatably mounted in the cleaner head. The difficulty associated with this arrangement is that the cradle must be sealed with respect to the cleaner head and this can be difficult to achieve.

EP1119282 addresses the problem one way and describes a cleaner head assembly doubly articulated with respect to the main body of the cleaner. This allows the brush housing to float freely on the surface to be cleaned even when the angle of inclination of the handle of the vacuum cleaner is altered during use. However, the constant movement and, in some cases, the weight of a motor on the brush bar can cause the brush housing to be lifted away from the floor surface. This is undesirable as the inlet suction becomes less effective.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a cleaner head which maintains the suction opening of the dirty air inlet in contact with the surface to be cleaned throughout cleaning. A further object of the invention is to maintain the dirty air inlet in a substantially horizontal plane, irrespective of the type of carpet being cleaned, the direction of movement of the cleaner head, the weight of any motor mounted on the brush housing and the angle of inclination of the handle to the vertical. The maintenance of the dirty air inlet in a horizontal plane ensures a good, even distribution of airflow through the inlet and around the brush bar. This in turn improves the pick-up performance of the cleaner head assembly. A still further object of the invention is a cleaner head for a vacuum cleaner which has improved pick-up capabilities.

The present invention provides a cleaner head assembly and a vacuum cleaner as broadly disclosed herein. Preferred features are set out in the detailed description.

The cleaner head assembly according to the invention is doubly articulated with respect to the main body of the vacuum cleaner and a resilient member biases the brush housing so as to urge the rear portion of the brush housing in an upward direction with respect to the cleaner head body.

The suction opening in the brush housing thus remains essentially in the optimum configuration, i.e. horizontal, and the pick-up performance of the cleaner is thereby improved. The brush housing is biased into the surface to be cleaned, against the force or weight of the brush housing and any motor for the brush bar which will tend to lift the front of the brush housing away from the surface to be cleaned during the normal forwards and backwards movement of the vacuum cleaner.

The preferred arrangement of the brush housing being pivotable with respect to the cleaner head body about an axis coincident with that of the brush bar is a convenient and easily manufactured construction.

The resilient member is preferably provided between the brush housing and the cleaner head body to counteract any lifting force acting on the brush housing. Preferably the resilient member acts between the cleaner head and the brush housing to pull the rear brush housing upwardly. More preferably the resilient member is provided between the cleaner head body and a rear portion of the brush housing and ensures that the suction opening of the dirty air inlet is maintained in contact with the surface to be cleaned at all times. This ensures reliable operation of the mechanism. The resilient member is preferably a tension spring.

A motor may be provided on the brush housing and arranged to drive the brush bar.

Preferably a flicker strip is provided to improve sealing of the suction opening with the surface to be cleaned and more preferably, a support strip or carpet strips are provided to improve the ability of the cleaner head assembly to pick up debris from carpet.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the invention will now be described with reference to the accompanying drawings, wherein:

FIG. 1 is a side view of a vacuum cleaner incorporating a cleaner head assembly according to the present invention;

FIG. 2 is a side view of the vacuum cleaner of FIG. 1 with the handle shown in an inclined position;

FIG. 3 is a side sectional view of the cleaner head of the cleaner of FIGS. 1 and 2 in an inclined position;

FIG. 4 is an underneath view of the cleaner of FIGS. 1 and 2;

FIG. 5 is a schematic sectional side view of the brush housing of the cleaner of FIGS. 1 and 2 in a rotated position;

FIG. 6 is an underneath view, shown on an enlarged scale, of the cleaner head, of the cleaner of FIGS. 1 and 2;

FIG. 7 a is a partial underneath view, shown on a further enlarged scale, of a central portion of the arrangement of the cleaner head of FIG. 6; and

FIGS. 7 b, 7 c and 7 d are cross sectional views through parts of the brush housing of the cleaner head of FIG. 7 a.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 and 2 illustrate the overall construction of an upright vacuum cleaner incorporating a cleaner head assembly according to the invention. The vacuum cleaner 100 has a main body 102 in which dust separation apparatus 104 is housed. In FIGS. 1 and 2 the dust separation apparatus 104 is shown schematically. The embodiment may comprise cyclonic dust separation apparatus consisting of two cyclones arranged in series. Apparatus of this type is well known and will not be described any further here because it has no material effect on the invention. A motor housing 106 is located at the lower end of the main body 102 and forms part of the main body 102. Supporting wheels 107 are mounted directly on the side of the motor housing 106. A cleaner head assembly 108 is rotatably mounted on the motor housing 106 about an axis A. The cleaner head assembly 108 has a brush housing 110 with a downward facing inlet 112 arranged at the forward end of the cleaner head assembly 108. A brush bar motor (not shown) is located within a motor housing 114. The motor housing 114 is mounted at the rear of the brush housing 110 and forms part of the brush housing 110. The motor is arranged with electrical connections (also not shown) suitable for driving a brush bar. A flexible duct extends between the brush housing 110 and a dirty air inlet in the main body 102 which communicates with ducting which leads to the dust separation apparatus 104.

A handle 116 extends upwardly from the lower part of the main body 102 and lies alongside the rear part of the main body 102. When the cleaner 100 is to be used in the upright mode (as shown in FIG. 1), the handle 116 extends upwardly beyond the main body 102 so that it can be gripped by a user and used to manoeuvre the cleaner 100 across a surface to be cleaned. The handle 116 is, however, releasable and may alternatively be used as a hose and wand assembly. This can be achieved in several ways and examples are shown and described in EP 0 037 674 and EP 0 134 654. The lower end of the hose/wand 116 is also connected via ducting 118 to the dirty air inlet of the main body 102 to allow dirt and dust entering the cleaner 100 via the hose and wand to be passed to the dust separation apparatus 104.

A changeover valve (not shown) is provided in order that the appropriate inlet can be automatically selected for different modes of operation. When the cleaner 100 is in the position shown in FIG. 1, the changeover valve automatically connects the dust separating apparatus 104 to the wand and hose 116 so that cleaner can be used in cylinder mode for above the floor cleaning. Air is drawn into the cleaner through the distal end 116 a of the wand which can be released from the cleaner for appropriate manipulation. The inlet 112 in the cleaner head assembly 108 is automatically shut off. When the cleaner 100 is to be used in conventional upright mode, the handle is restored to the position shown in FIG. 1 and then inclined to the vertical as shown in FIG. 2. The changeover valve automatically shuts off the air inlet at the distal end 116 a of the wand and connects the dust separating apparatus 104 to the inlet 112 in the cleaner head assembly 108. The construction of the changeover valve does not form part of the present invention and will not be described any further here.

In all cases, ie in the upright mode and in the cylinder mode, a motor (not shown) located in the motor casing 106 drives a fan (also not shown) so as to draw air into the cleaner 100 via the appropriate inlet, conduct it to the dust separating apparatus 104 in the main housing 102 and then expel the cleaned air to the atmosphere. The cleaned air is preferably caused to flow past the motor so as to cool it before being expelled.

FIGS. 3 and 4 show in more detail the cleaner head assembly 108 forming part of the vacuum cleaner 100 shown in FIGS. 1 and 2. The cleaner head assembly 108 has a cleaner head body 10 comprising a front portion 12 extending laterally across the width of the vacuum cleaner 100 and two rearwardly extending side arms 14 extending rearwardly from the side portions of the front portion 12. Each side arm 12 has a lug (not shown) which defines an aperture centred on the axis A about which the cleaner head assembly 108 is pivotably mounted on the motor casing 106. The cleaner head assembly 108 is mounted on the motor casing by way of pins which extend through the apertures in the lugs. The cleaner head assembly 108 pivots freely about the axis A so as to “float” on the floor to be cleaned without requiring the user to identify and set a predetermined level at which the cleaner head must operate.

The cleaner head assembly 108 includes a brush housing 110. The brush housing 110 is pivotably mounted on the front portion 12 of the cleaner head body 10 by way of lugs (not shown) depending from the side portions of the front portion 12. The brush housing 110 is manufactured from an upper plate 20 and a lower plate 22 which may be made from plastics material or a metal such as stainless steel. The upper and/or the lower plate may be transparent.

The upper and lower plates 20, 22 are joined together by quarter turn fasteners (not shown), by press-fitting or by other suitable means. A seal 24 is trapped between the upper and lower plates 20, 22 so as to ensure that the seal between the plates 20, 22 is essentially airtight. Rollers 25 are rotatably mounted at the front edge of the lower plate 22 to support the brush housing 110 on the carpet or other surface to be cleaned. The rollers 25 can be positioned at or adjacent the outer edges of the lower surface 22 or, alternatively, can either extend continuously or in a spaced manner across the entire width of the brush housing 110.

A suction opening 112 is formed in the lower plate 22. The suction opening 112 extends across the entire width of the brush housing 110. A brush bar 26 is rotatably mounted in the brush housing 110 so that the bristles 27 of the brush bar 26 protrude slightly out of the suction opening 112. The axis B about which the brush bar 26 rotates is coincident with the axis about which the brush housing 110 is pivotably mounted on the front portion 12 of the cleaner head body 10. The brush bar 26 is arranged to be drivable by the brush bar motor by a direct drive train mechanism, for example. Other drive mechanisms and arrangements, for example, where the brush bar is arranged to be drivable by the motor of the vacuum cleaner 100, by way of a drive belt, are possible. The upper plate 20 of the brush housing 110 has a connection opening 28 for connecting the brush housing 110 to an air inlet on the main body of the vacuum cleaner 100.

A hooked projection 34 is provided on the rear of the interior surface of the front portion 12 of the cleaner head body 10. The hooked projection 34 extends forwardly and upwardly as shown in the drawings. An eye projection 36 is also provided on the upper surface of the lower plate 22 of the brush housing 110. The eye projection 36 is located forwardly of the hooked projection 34. The eye projection 36 is located downwardly of the axis B about which the brush housing 110 is pivotably mounted on the cleaner head body 10. The hook projection 34 is located upwardly of the axis B. A resilient member 38 extends between the hooked projection 34 and the eye projection 36. The resilient member 38 takes the form of a tension spring.

The suction opening 112 in the lower plate 22 is substantially rectangular in shape and is delimited by side walls 52, 54 and end walls 56 and 58. An arm 50 is provided extending rearwardly from wall 52 at the front of the suction opening 112 to wall 54 at the rear of the suction opening 112. The inner surface of the arm 50 is domed or comprises an alternative shape suitable for accommodating the brush bar 26 so that the bristles of the brush bar protrude slightly out of the suction opening 112. In the preferred embodiment more than one arm 50 is provided, preferably four. The arm or arms 50 may be made from plastics material or a metal such as stainless steel. The preferred embodiment is illustrated in FIGS. 6 and 7. A first end 51 of the arm 50 joins the front portion of the suction opening 112. A second end 53 of the arm 50 joins the rear portion of the suction opening 112. The ends 51, 53 join the walls 52, 54 of the suction opening at substantially the same height and level and flush to the walls 52, 54. A portion 70 of arm 50 extends away from the plane of the suction opening, towards the surface to be cleaned.

A cross section (FIG. 7 b) taken through the mid-point of an arm 50, at axis A-A shows the shape of the arm and the detail of portion 70. FIGS. 7 c and 7 d, show cross sections through an arm 50 at axis B-B of the portion 70 and at axis C-C of the lower portion of arm 50. The arm 50 is shaped with a cross section that varies gradually and smoothly from the front of the suction opening 112 to the rear of the suction opening 112. The outer surface of the arm 50 closest, in use, to the surface to be cleaned presents a surface shaped and dimensioned to assist and aid the movement of the brush housing 110 and the cleaner head 108 over surfaces to be cleaned. The arm 50, also known as a carpet or rug strip or support member allows the brush housing 110 to sink and lower into deep pile carpet, but to be supported over a hard surface or short pile carpet. The suction opening is therefore not forced down by excessive suction force on a hard surface as the shaped arms hold the lower plate 22 away from the surface and again the cleaner maintains good pick-up performance.

A sealing member 40 is provided on the rear of the brush housing. FIGS. 4, 5 and 6 show in more detail the brush housing 110 and sealing member 40 forming part of the vacuum cleaner 100 shown in FIGS. 1 and 2. The operation of the sealing member 40 will be described further below. The resilient member 38, the arm(s) 50 and the sealing member 40 operate in combination to assist the pick up performance and cleaning efficiency of the vacuum cleaner.

FIG. 3 illustrates the orientation of the cleaner head assembly 108 on a surface such as carpet, and in particular deep pile carpet. The bristles 27 of the brush bar 26 protrude slightly beyond the suction opening 112 into the carpet pile and the cooperation of the carpet pile with the bristles helps to maintain a gap in between the surface to be cleaned and the brush housing, the gap allows for the ingress of large debris into the air inlet. In the preferred embodiment the gap is a maximum of 3 mm, this preferred spacing provides an opening sufficient to allow dirt, dust and large debris to be sucked into the air inlet whilst maintaining a high suction performance.

FIG. 5 illustrates the orientation of the brush housing 110 on a surface such as a hard floor or a short pile carpet. FIG. 5 shows that the upward force exerted on the brush housing 110 by the resilient member 38 is greater than the downwards force on the rear of the brush housing 110 exerted by the brush bar motor and motor housing 114. On a shorter pile carpet the bristles 27 of the brush bar 26 are not supported by the carpet pile as in the situation shown in FIG. 3. This means that the suction force can act to urge the front of the suction opening 112 into the surface and act effectively to block the front of the air inlet and suction opening to dirt and debris. The rotation of the brush housing creates a gap at the rear of the suction opening 112 which further degrades the performance of the cleaner head. The gap may be sealed by a sealing member.

The sealing member 40 is located adjacent the suction opening 112 and extends across the entire width of the suction opening 112. A first portion 42 of the sealing member is located in slot 46 in the lower plate 22. The first portion 42 is secured and fixed in the slot 46 by any suitable means. A second portion 44 of the sealing member 40 depends from the first portion and is free to move between a first position lying flush and close to a lower surface of the lower plate 22 (shown in FIG. 3) and a second position extending downwardly from the brush housing 110. The sealing member 40 is mounted in the lower plate 22 of the brush housing 110 so that a free end 45 is capable of protruding below the suction opening 112.

The sealing strip 40 is moveable between the first position and the second position by any suitable means. This could be by a rotatable connection at the brush housing. Alternatively, and preferably, the sealing member comprises a resilient and deformable material such as rubber or plastic material. The sealing member is therefore capable of bending and taking a set to lie flush to the lower plate 22 as shown in FIG. 3. The sealing member is also capable of being deformed and brought into the substantially straight orientation shown in FIG. 5. This aids sealing of the suction opening and maintains performance of the cleaner head.

The function of the resilient member 38 is to bias the brush housing 110 in a clockwise direction so that the rear portion of the brush housing 110 is raised upwardly. At all times, the tension spring 38 acts between the brush housing 110 and the cleaner head body 10 so as to bias the rear portion of the brush housing upwardly. The rear portion of the brush housing 110 is therefore biased against the weight of the motor housing and motor and maintained in contact with the surface to be cleaned. It will also counteract any lifting forces which might otherwise cause the front portion of the brush housing 110 to be lifted away from the surface to be cleaned. Lifting forces caused by a thick pile carpet or, for example, due to large debris or friction forces may exert a lifting force on the brush housing 110. In addition because the flexible tube 32 is made from a plastics material, the tube 32 may, under some circumstances, exert some force on the rear portion of the brush housing 110 during normal use of the vacuum cleaner 100.

The resilient member is designed and arranged to counteract the downward force exerted on the rear of the brush housing 110 by the weight of the brush bar motor and motor housing 114. Thus the cleaner head assembly 108 and brush housing 110 are specifically and deliberately designed to ensure that the brush housing 110 remains horizontal, or at least the suction opening 112 arranged in the lower plate 22 remains in a horizontal plane, at all angles of inclination of the handle 116 to the vertical and on all surfaces during normal use of the vacuum cleaner 100 in order to maintain maximum performance.

Maintaining the suction opening in a horizontal plane maximises the efficacy of the cleaner head assembly during on the floor cleaning. The brush housing is no longer influenced by external factors such as differing carpet piles, direction of cleaner movement and differing angles of inclination of the handle to the vertical so that the brush housing can be tilted and the suction opening lifted away from the floor, at least on one side. Maintaining the suction opening in a horizontal plane maintains good suction through the fibres of the carpet being cleaned and thus maintains good pick-up by the cleaner head.

The action of the resilient member 38 in combination with the operation and movement of the sealing member 40 enhances the performance of the cleaner head. The function of the sealing member 40 is to assist in maintaining a sealed and closed air inlet at the suction opening 112 by closing a gap between the rear portion of the brush housing and the surface to be cleaned. Maintaining a good seal around the suction opening maintains good suction through the fibres of the carpet being cleaned and thus maintains good pick-up.

The invention is not limited to the precise details of the embodiment disclosed above. Modification not affecting the essence of the invention are intended to be included within the scope of the invention. For example, the tension spring could be replaced by any resilient member and the seal around the connection point 28 could be formed by any airtight material. The sealing flicker strip could be formed of any suitable material for example plastics or rubber and could be attached to the housing by any suitable means, for example, by adhesive, a snap-fit catch or other fixings. The sealing flicker strip could be moveably attached to the housing by any suitable means for example by pivoting, sliding or other fixing. In addition the skilled reader will understand that the number, arrangement and shaping of carpet or rug strips on the underside of the brush housing could be altered. Other modifications and variations will be apparent to a skilled reader. 

1. A cleaner head assembly for a vacuum cleaner comprising a cleaner head body pivotably attachable to a main body of a vacuum cleaner and a brush housing pivotably mounted on the cleaner head body, the brush housing having a suction opening and a brush bar mounted therein, and a resilient member arranged to bias the brush housing in a direction of pivoting so as to urge a rear portion of the brush housing in an upward direction with respect to the cleaner head body, the cleaner head assembly further comprising a sealing member extending downwardly from the rear portion of the brush housing so as to provide a seal between the housing and a floor surface in use.
 2. A cleaner head assembly as claimed in claim 1, wherein the brush housing is pivotable with respect to the cleaner head about an axis coincident with an axis of rotation of the brush bar.
 3. A cleaner head assembly as claimed in claim 2, wherein the axis of the brush bar is located in a front portion of the brush housing.
 4. A cleaner head assembly as claimed in claim 1, 2 or 3, wherein the resilient member is located between the cleaner head body and the brush housing.
 5. A cleaner head assembly as claimed in claim 1, 2 or 3, wherein the resilient member is adapted to maintain the suction opening in a horizontal plane.
 6. A cleaner head assembly as claimed in claim 1, 2 or 3, wherein the resilient member extends between the cleaner head body and a rear portion of the brush housing and exerts an upward force on the rear portion of the brush housing.
 7. A cleaner head assembly as claimed in claim 1, 2 or 3, wherein the resilient member comprises a tension spring.
 8. A cleaner head assembly as claimed in claim 1, 2 or 3, wherein a motor is provided to drive the brush bar.
 9. A cleaner head assembly as claimed in claim 8, wherein the motor is mounted to the brush housing.
 10. A cleaner head assembly as claimed in claim 1, 2 or 3, wherein the sealing member comprises a flicker strip.
 11. A cleaner head assembly as claimed in claim 1, 2 or 3, wherein the lower portion of the cleaner head comprises a support member arranged to extend across the suction opening.
 12. A cleaner head assembly as claimed in claim 11, wherein the support member is profiled so as to adjust the relationship between the main body of a vacuum cleaner, the cleaner head body and the brush housing relative to the horizontal plane of the suction opening.
 13. A vacuum cleaner comprising a main body including the cleaner head assembly as claimed in claim 1, 2 or 3, wherein the cleaner head body is pivotably mounted on the main body of the vacuum cleaner.
 14. A vacuum cleaner as claimed in claim 13, wherein the support member has a profile such that, in use, the suction opening remains horizontal as vacuum cleaner moves along a surface.
 15. (canceled) 